The present invention relates to a light-sensitive mixture, which becomes soluble by exposure, comprising
(a) a 1,2-quinonediazide or a mixture of PA1 (b) a water-insoluble binder soluble in aqueousalkaline solutions, PA1 (c) a photolytically cleavable organic halogen compound, and PA1 (d) a dyestuff. PA1 X denotes a halogen atom; and PA1 X denotes a halogen atom, and
(a.sup.1) a compound forming an acid on exposure and PA2 (a.sup.2) a compound having at least one C--O--C bond cleavable by acid,
After exposure, the mixture shows a clearly visible color contrast between exposed and unexposed areas.
Mixtures of the generic type indicated are preferably used for preparing planographic printing plates and photoresists, and such mixtures are known, for example, from U.S. Pat. No. 3,969,118. The mixtures described there contain as the dyestuff (d) a triphenylmethane, azine or anthraquinone dyestuff and as the organic halogen compound (c) a 1,2-naphthoquinone-2-diazide-4-sulfonyl halide. After image exposure they produce an image contrast which is clearly visible in daylight or in white artificial light. However, the image contrast is less pronounced, and in some cases inadequate under the yellow safety light customarily used when working with reprographic materials.
U.S. Pat. No. 3,929,488 describes corresponding mixtures which contain certain azo dyestuffs as the dyestuffs and diazonium salts of strong acids as the acid donors. These mixtures produce only a relatively slight visual contrast in normal light and in safety light.
U.S. Pat. No. 4,163,672 and British Patent No. 2,005,855 describe similar mixtures which contain diazonium salts as the acid donors and azo, triphenylmethane, azine or anthraquinone dyestuffs as the dyestuffs. Their contrast is likewise frequently inadequate in yellow safety light.
U.S. Pat. No. 4,160,671 describes corresponding mixtures which contain trihalogenomethyls-triazines or trihalogenomethyl-2-pyrones as the acid donors and azine, triphenylmethane or anthraquinone dyestuffs as the dyestuffs. The properties of these mixtures are similar to those of the abovementioned mixtures.